1. Field of the Invention
The present invention relates to a heat and impact resistant thermoplastic resin composition. More particularly, it relates to a resin composition obtained by incorporating into a polyamide resin a rubber-modified resin prepared graft-copolymerizing an N-substituted maleimide-containing monomer to a conjugated diene rubber, which is capable of providing a molded product having excellent heat resistance and particularly excellent impact resistance.
2. Discussion of Background
Polyamide resins have excellent abrasion resistance, electrical properties, mechanical strength and chemical resistance. Therefore, their molded products have been used for various mechanic parts as engineering plastics. However, they have drawbacks such as large water absorbance, low heat resistance and low impact resistance, particularly low notched impact strength. Further, they also have drawbacks that they are inferior in rigidity upon absorption of moisture and in molding processability.
Since the polyamide resins have such drawbacks, their use as engineering plastics is limited, and in some cases, their excellent properties can not be adequately utilized.
In order to overcome these drawbacks of the polyamide resins, for example, it has been proposed to mix an acrylonitrile-butadiene-styrene copolymer (ABS resin) to polyamide resin to obtain a blend resin composition (e.g. Japanese Examined Patent Publication No. 23476/1963). However, such a blend resin composition of a polyamide resin with an ABS resin is inferior in the compatibility, and when formed into a molded product, it brings about drawbacks such that a lamellar peeling phenomenon is likely to result due to inadequate compatibility, and the mechanical strength is likely to substantially deteriorate e.g. as lacking in toughness. Under the circumstances, as a method for improving the compatibility of the polyamide resin with a styrene-type polymer such as an ABS resin, it has been proposed to incorporate a styrene-type polymer containing an a .alpha.,.beta.-unsaturated carboxylic anhydride component as a third component to the blend resin composition composed of both resins (e.g. Japanese Examined Patent Publication No. 47304/1985). By the incorporation of this third component, it is certainly possible to obtain a blend resin composition wherein the polyamide resin and the styrene-type polymer are physically finely dispersed. However, no substantial improvement in the heat and impact resistance is obtainable with such a three component resin composition.
As described in the foregoing, among the conventional resin compositions composed of a polyamide resin and a styrene-type polymer, there has been no resin material which has not only excellent properties of both resins but also excellent heat and impact resistance.